Fireproof building structures have a low risk of catching fire, and even after they catch fire, the main structural parts thereof, for example, walls, posts and crossbeams, will not show a decrease in strength, and thus the building structures that caught fire can be reused after simple repair. For this reason, the Enforcement Decree of the Korean Building Act provides the standards of fireproof structures for each of the main structural parts of buildings, for example, walls, posts, bottoms, crossbeams, roofs and stairs.
However, due to the rapid development of new building materials, advanced countries discard the way of providing the specific standards of fireproof structures for each part of the structures, and adopt the way of determining the performance of each structural part, which can resist fire for a specific time. In the case of Japan, for example, the Enforcement Decree of the Building Act includes the same contents as those of the Enforcement Decree of the Korean Building Act, but currently provides that the main structural parts of a building can resist fire for 30 minutes to 3 hours depending on the position of the building, such as the number of layer of the building.
As cores for fire doors or various building structures, materials having honeycomb or urethane foam inserted therein, or materials comprising glass fiber or rock wool, have been used. However, such materials are harmful for the human body and have low insulation properties, and thus do not sufficiently satisfy refractory standards that gradually tighten.
As another example, there is a case in which a fire door is manufactured using, as a single core, urethane, polyimide or polystyrene foam resin, which contain an inorganic additive such as a flame retardant. However, these core materials, when caught fire, have low ignition point, leading to low flame-blocking and insulation effects, and generate poisonous gas, thus causing human loss.
Korean Patent Registration No. 528391 (Publication No. KR 10-528391) discloses a material for use as cores for fire doors or as internal/external materials or cores for various building structures, which is prepared by melting and spinning basalt to make basalt fiber, mixing the basalt fiber as a main component with bentonite, soda-silicate, and polyvinyl acetate emulsion at a specific ratio, and moulding the mixture in the form of a panel or sheet. According to the disclosure of said patent, the material is harmless for the human body, does not generate dust during operations, has excellent heat resistance and insulation properties, generates a reduced amount of poisonous gas when caught fire, emits a large amount of far-infrared rays, and has good sound-absorbing properties.
Also, calcined bauxite has been used as one of main raw materials in the refractory material industry. Ghana produced most of the worldwide demand of bauxite up to the late 1970s, and Refractory A-grade super calcined bauxite commercially available from Linden Corp. was acknowledged as an industrial standard. Currently, China dominates the refractory bauxite market and supplies 70% of the worldwide demand of bauxite. Such calcined bauxite has an alumina (Al2O3) content of more than 90%.
The present inventors have made efforts to develop a refractory, which minimizes the harmful effects of the prior refractory materials and, at the same time, has excellent refractory properties. As a result, the present inventors have found that, an aqueous flame-retardant composition obtained by adding an aluminum hydroxide silicate mineral, having a highly expandable layered structure, to an inorganic flame retardant consisting of a phosphorus-based flame retardant, a first metal oxide and a second metal oxide containing silicon dioxide, and the balance of water [see Korean Patent Registration No. 520814 (Publication No. KR 10-520814)], shows excellent refractory properties by forming closed pores and blocking oxygen due to gas resulting from the thermal self-decomposition of the phosphorus-based flame retardant and, at the same time, maintains the properties of the aqueous flame-retardant composition. Also, we have found that a refractory board formed using this inorganic expandable refractory composition will have excellent refractory properties, thereby completing the present invention.